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Kubanek, Julia

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Chemically mediated competition between microbes and animals: microbes as consumers in food webs

2006-11 , Burkepile, Deron E. , Parker, John D. , Woodson, Clifton Brock , Mills, Heath Jordan , Kubanek, Julia , Sobecky, Patricia A. , Hay, Mark E.

Microbes are known to affect ecosystems and communities as decomposers, pathogens, and mutualists. However, they also may function as classic consumers and competitors with animals if they chemically deter larger consumers from using rich food-falls such as carrion, fruits, and seeds that can represent critical windfalls to both microbes and animals. Microbes often use chemicals (i.e., antibiotics) to compete against other microbes. Thus using chemicals against larger competitors might be expected and could redirect significant energy subsidies from upper trophic levels to the detrital pathway. When we baited traps in a coastal marine ecosystem with fresh vs. microbe-laden fish carrion, fresh carrion attracted 2.6 times as many animals per trap as microbe-laden carrion. This resulted from fresh carrion being found more frequently and from attracting more animals when found. Microbe-laden carrion was four times more likely to be uncolonized by large consumers than was fresh carrion. In the lab, the most common animal found in our traps (the stone crab Menippe mercenaria) ate fresh carrion 2.4 times more frequently than microbe-laden carrion. Bacteria-removal experiments and feeding bioassays using organic extracts of microbe-laden carrion showed that bacteria produced noxious chemicals that deterred animal consumers. Thus bacteria compete with large animal scavengers by rendering carcasses chemically repugnant. Because food-fall resources such as carrion are major food subsidies in many ecosystems, chemically mediated competition between microbes and animals could be an important, common, but underappreciated interaction within many communities.

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Ambiguous role of phlorotannins as chemical defenses in the brown alga Fucus vesiculosus

2004-08-16 , Kubanek, Julia , Lester, Sarah E. , Fenical, William , Hay, Mark E.

Brown seaweeds (Fucales) produce phlorotannins that are often considered chemical defenses against herbivores. The many correlative and fewer direct tests conducted have shown effects of phlorotannins on herbivore feeding behavior to be variable. In an attempt to clarify the roles of phlorotannins versus other metabolites in defending brown algae, we conducted bioassay-guided fractionation of herbivore-deterrent extracts from the commonly studied brown alga Fucus vesiculosus. Feeding by the amphipods Ampithoe valida and A. longimana and the sea urchin Arbacia punctulata was suppressed by crude and water-soluble extracts of F. vesiculosus, but this deterrence was lost following storage or fractionation of the active, water-soluble extract. Phlorotannins in these extracts did not decompose in parallel with the loss of feeding deterrence. F. vesiculosus phlorotannins were fed to herbivores at 3 to 12× the isolated yield (or 4.2 to 16.8% of plant dry mass). No herbivore was deterred from feeding by concentrations of 3 or 6×, but A. valida (the only test herbivore that readily consumes F. vesiculosus in the field) was deterred at 12× isolated yield. When juvenile A. valida were raised on an artificial diet containing F. vesiculosus phlorotannins at 3× isolated yield, the phlorotannin-rich diet significantly enhanced, rather than reduced, amphipod survivorship and growth relative to an equivalent diet without phlorotannins. Females ovulated only on the phlorotannin-rich diet. Compounds other than phlorotannins appear to defend the F. vesiculosus populations we investigated, but we were unable to identify these unstable compounds.

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Drugs from the Sea

2006-08-26 , Ludovice, Peter J. , Hunt, William D. , Kubanek, Julia

Our guest Prof. Julia Kubanek from the School of Biology and the School of Chemistry and Biochemistry at Georgia Tech will discuss how pharmaceutical agents can be extracted from marine organisims.

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Palatability and defense of some tropical infaunal worms: alkylpyrrole sulfamates as deterrents to fish feeding

2003-11-28 , Kicklighter, Cynthia Ellen , Kubanek, Julia , Barsby, Todd , Hay, Mark E.

Numerous studies have investigated chemical defenses among sessile species growing on hard substrates, but few have addressed this for mobile species in soft-sediment communities. We investigated the palatability and potential chemical defenses of 11 worm species from soft-sediment systems in southern Florida, USA. Three species were unpalatable to the bluehead wrasse Thalassoma bifasciatum. The polychaete Cirriformia tentaculata and the hemichordate Ptychodera bahamensis were uniformly unpalatable. For the polychaete Eupolymnia crassicornis, the exposed tentacles were unpalatable, but the body, which remains protected in a deeply buried tube, was palatable. These unpalatable worms were chemically defended; extracts of C. tentaculata, P. bahamensis, and the tentacles of E. crassicornis deterred fish feeding. For C. tentaculata, bioassay-guided fractionation demonstrated that a mixture of 3 closely related alkylpyrrole sulfamates deterred fish at naturally occurring concentrations (2-n-hexylpyrrole sulfamate [1.6% of worm dry mass], 2-n-heptylpyrrole sulfamate [3.1% dry mass], and 2-n-octylpyrrole sulfamate [0.8% dry mass]). This appears to be the first documentation of characterized natural products defending a marine worm from consumers. For P. bahamensis and the tentacles of E. crassicornis, deterrent effects of crude extracts decomposed before specific compounds could be identified

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Chemical Cues in the Ocean

2006-04-25 , Kubanek, Julia

We are all at the mercy of molecules: hormones affect our sexual interests, toxins give us food poisoning, polluting chemicals give us asthma, and the smell of Krispy Kreme tugs on the steering wheel whenever we drive along Ponce de Leon Ave. Molecules play an even greater role in the lives of marine plants, animals, and microorganisms. On coral reefs and in the open ocean, chemicals affect who eats who, who settles down next to who, and who can fight off a potentially deadly infection. In lab and field experiments, Georgia Tech faculty and students are working to understand the role of natural chemical compounds in the survival and reproduction of marine organisms.

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